Rush Limbaugh is probably the single media figure that the left hates the most. He's the most successful radio personality, ever. He has an audience in the tens of millions, and starting in ~1989, he created the first major break in the leftist media monopoly.
The left endlessly villifies him, because they will never, ever forgive him for that.
Drudge isn't that big a deal at this point, but he was critical for the uprising of internet-based media; he's the one who broke the story of the Monica Lewinskey scandal in the 90's, after conventional television media deliberately did not report on it for months.
I don't watch Fox myself, but I'm not unaware of how important it has been for breaking cultural hegemony in television media.